In the chemical industry, petroleum, metallurgy and electricity, high temperature dusty gases are usually generated. Since various processes need to recover the energy and reach the environmental protection discharge standard, dust removal shall be done to the high temperature dusty gases. The high temperature dust removal is a technology that directly performs a gas-solid separation under high temperature to purify the gas, which can furthest utilize the sensible physical heat, the potential chemical heat and the kinetic force of the gas and improve the energy utilization rate, while simplifying the technological processes and saving the device investment.
The device usually used for the high temperature gas-solid separation is a gas filter, and the filter tube is the core element of the gas filter. The sintered metal filter tube has good performances in anti-seismic, the high-temperature resistance, the corrosion resistance and thermal impact, and also has high filtration precision and filtration efficiency, thus it is widely used in the field of high temperature gas purification.
As illustrated in FIG. 8A, which is a sintered metal filter tube 902 used in the prior art. The filter tube 902 is a cylinder with one end opened, and the other end closed. The opening end is provided with a flange to be fixed on the tube sheet of the filter.
As illustrated in FIG. 8B, which is a structure diagram of an existed filter 900, wherein a tube sheet 903 of the existed filter 900 hermetically divides the filter into two parts: an upper clean gas side and a lower dusty gas side. The dusty gas (also referred to as coarse synthesis gas) enters the lower dusty gas side of the filter from a gas inlet 901 of the filter 900, and reaches each filtration unit under the gas driving force. During the filtration process, the dusty gas enters the filter tube under the effect of a pressure difference from an outer surface of the filter tube 902 through the pores in the filtration material. The solid particles in the gas are intercepted on the outer wall of the filter tube 902 to form a pressed powder layer 9021 (see FIG. 8C). The clean gas is discharged from the opening end of the filter tube to enter the clean gas side, and then discharged via the gas outlet 905 for subsequent process. Along with the filtration operation, the pressed powder layer 9021 on the outer surface of the filter tube 902 gradually become thicker, thus the pressure drop of the filter 900 increases. In that case, pulse-jet cleaning shall be adopted to reproduce the performance of the filter tube. When dust removal is carried out through pulse-jet cleaning, a pulse-jet valve 908 normally closed is opened, and the high-pressure nitrogen or clean synthesis gas instantaneously enters a pulse jet pipeline 907; next, the high-pressure and high-speed pulse-jet gas is ejected into the corresponding ejector 904 through a nozzle 906 in the pipeline; the pulse-jet gas enters the corresponding filter tube 902, and peels off the pressed powder layer 9021 on the outer surface of the filter tube 902 using the transient energy (see FIG. 8D), so that the resistance of the filter tube substantially recovers to the initial state, thereby realizing the performance reproduction of the filter tube.
The support (or referred to as framework) of the existed filter tube is made of sintered metal powder or sintered metal fiber material. The filter tube has a height L1 and an outer diameter D1 (see FIG. 8A), which performs a filtration through the micro-pores of the filter tube, and realizes the performance regeneration in a manner of pulse-jet.
However, the filter tube used by the prior art at least has the following defects:
(1) The filtration area of the single filter tube is limited, and the filtration capacity of the whole filter is small.
The filtration area of the single filter tube means an outer surface area of the filter tube. In a large-scale gas filter, usually several hundreds to more than ten hundreds of filter tubes are mounted. When the amount of treated process gas increases, the number of required filter tubes increases, the volume of the filter becomes huger, and the production cost and the maintenance fee of the whole device are very high.
(2) The pulse-jet process causes serious “backflow”.
Studies show that when the pulse-jet is going to be ended, the speed of the pulse-jet gas gradually decreases. In this process, the pressure in the filter tube is smaller than the pressure outside. The gas near the outer wall of the filter tube flows back from the outside of the tube to the inside of the tube through the tube wall, and the solid particles blown off from the outer wall of the filter tube again deposit on the outer wall. This “backflow” phenomenon even causes some tiny particles to be embedded into the tube wall, and the porous passage of the filter tube may easily be blocked, thus the service life of the filter tube is reduced.
(3) The outer surface of the support is the filtration surface. In the filtration process, the tiny particles in the dusty gas may easily deposit inside the support. Since the porous passage of the filter tube is an irregular labyrinth, the pulse-jet operation is also difficult to blow out the deposited dust, thus the pores of the filter tube may be blocked and invalid.
(4) Studies show that when dust removal is performed for the filter tube through pulse-jet, since the opening at the top of the filter tube form an ejector structure together with the pulse jet gas flow, the high-pressure and high-speed pulse-jet gas flow may eject clean gas into the filter tube from the vicinity of the opening of the filter tube, and a “negative pressure region” may easily occur near the opening. The negative pressure region causes the dust outside the filter tube to be entrained onto the surface of the filter tube. The region is corresponding to the dust removal dead zone, and the dust removal cannot be achieved.
Therefore, by virtue of the experiences and practices of many years in related industries, the inventor proposes a filter tube for high temperature gas-solid separation and its filtration device, so as to overcome the defects of the prior art.